Absorption measurement systems are applied today in a large number of industrial applications, especially in the chemical and biochemical industries as well as in water or waste water processing, for measuring absorption characteristics both on line as well as for removed samples. In the case of measuring samples, the measuring chamber regularly has a cuvette fillable with a sample of the medium; the cuvette is inserted into the measuring arrangement and irradiated through a correspondingly placed window of the measuring arrangement. Along with that, there are also absorption measurement systems, which suck the medium into the measuring chamber. In on line measuring, the measuring arrangement is embodied, for example, as a probe, which is brought into the medium. Here the measuring chamber is formed by a cavity in the probe; the cavity is filled by the medium, and the cavity is irradiated through windows mounted on opposite sides of the cavity.
Absorption measurements are executed in different frequency ranges, especially the visible range, the ultraviolet range, or the infrared range under the application of corresponding monochromatic or multifrequency transmission units, depending on application.
The measuring of the radiation intensities emerging from the measuring chamber as a function of the absorption in the medium can occur integrally over a predetermined frequency range or via a spectrometer as a function of frequency.
Absorption coefficients of the medium are regularly measured using absorption measurement systems; for example, the absorption coefficients are determined for a predetermined frequency, as a function of frequency for a predetermined frequency range, or as a variable averaged over a predetermined spectral range.
Other properties, which are reflected in the absorption behavior of the medium, can be determined on the basis of these absorption coefficients using corresponding evaluation methods; such properties include e.g. substances determined to be contained in the medium and/or the concentration of such substances, as well as properties such as e.g. turbidity or coloring. Moreover, other properties, such as e.g. the total organic carbon content or the chemical oxygen demand of the medium can also be derived using corresponding evaluation methods.
Described in U.S. Pat. No. 6,956,648 B23 is an absorption measurement system, embodied as a spectrometric probe, for measuring a property of a medium reflected in the absorption behavior of the medium. The system comprises:                a measuring chamber filled with the medium in measurement operation,                    in which radiatable measuring paths of equal length extend completely through the medium;                        a transmitting unit, which transmits radiation along the measuring paths through the measuring chamber in measurement operation;        a measuring and receiving unit,                    which receives radiation passing through the measuring chamber on the measuring paths and measures its radiation intensities passing through the measuring chamber dependent on the property of the medium; and                        a measuring electronics, which determines the property based on the measured radiation intensities and the length of the measuring paths.        
A reference chamber bordering the measuring chamber and likewise filled in measurement operation with the medium is additionally provided in the probe described here; reference paths of equal length extend through the reference chamber parallel to the measuring paths in the measuring chamber; the reference paths are shorter than the measuring paths. Changes of the measuring arrangement, such as e.g. age-related changes of the transmission power of the transmission system or the optical transmission systems of the absorption measurement system, are here recognized through a comparison of the optical spectra of the radiation penetrating the measuring chamber on the measuring paths relative to the radiation penetrating the reference chamber on the reference paths.
Absorption measurement systems of the type cited above basically have the problem that the measuring range and the accuracy of measurements achievable in the measuring range depend in high measure on the predetermined length L of the measuring paths. The cause of this is that the radiation intensity I0 emitted by the transmitting unit falls over the predetermined length L of the measuring path in the medium exponentially with the absorption coefficient μ of the medium. For the radiation intensity I striking the measuring and receiving unit and measured by the measuring and receiving unit, the following equation accordingly applies:I=I0e−μL 
Therewith, the measuring range and the achievable accuracy of measurements in the measuring range are fixed by the accuracy, with which the logarithm of the ratio of the transmitted radiation intensity I0 to the measured radiation intensity I divided by the length L of the measuring paths can be determined.
Due to the limited dynamics of today's measuring and recording units, measurements are only possible when the measurement effect, i.e. the difference between the transmitted radiation intensity I0 and the measured radiation intensity I, is sufficiently large, and the absolute values of the transmitted radiation intensity I0 and the measured radiation intensities I lie in a metrologically registerable value range.
As a result, the exact measurement of smaller absorption coefficients μ requires a large length L of the measuring paths, while the exact measurement of large absorption coefficients μ requires a comparatively small length L of the measuring paths.
The means that the user can only operate the absorption measurement system in a narrowly limited measuring range due to the predetermined length L of the measuring paths, and the accuracy of measurement achievable sinks toward the edge of the already narrowly limited measuring range.
The field of use of absorption measurement systems with a predetermined measuring path of length L is limited in this way. A flexible use of one and the same absorption measurement system in applications differing as regards the absorption coefficients μ to be measured is not, as a rule, possible.